Abstract

Background: Tumors often demonstrate initial responses to cisplatin-based chemotherapy in treating non-small cell lung cancer (NSCLC), but eventually develop resistance and limit the success of therapy. We investigated whether IL-6 signaling is important in developing cisplatin-resistance of NSCLC and explore if targeting IL-6 signaling may increase tumor sensitivity to cisplatin.

Methods: We performed in vitro cytotoxicity test using the IL-6 knocked down and scramble (sc) control A549 and H157 NSCLC cell lines (A549IL-6si/sc and H157IL-6si/sc). We also performed in vivo mice studies by establishing xenografts using the A549IL-6si/sc cell set. We next examined the mechanism by which IL-6 mediates cisplatin resistance by performing studies of qPCR, Western analyses, and applying inhibitors of intracellular signaling molecules. Finally, we independently developed the cisplatin resistant A549 (A549CisR) and H157(H157CisR) cell lines and investigated whether targeting IL-6 signaling using a neutralizing antibody of IL-6 could prime these cicplatin-resistant cells to increase the sensitivity to cisplatin.

Results: The in vitro survival tests revealed that cisplatin was more cytotoxic to the IL-6 knocked down A549IL-6si and H157IL-6si cells than sc control cells. In in vivo mice studies, we consistently observed more effective tumor regression in A549IL-6si cells-derived xenografts than sc cells-derived tumors (control) after cisplatin treatments. In mechanistic studies, we found that expressions of the anti-apoptotic proteins (Bcl-2 and Mcl-1) and the molecules associated with DNA repair (ATM, CHK1, TP73, p53, and ERCC1) were significantly increased upon cisplatin treatment in A549sc and H157sc cells, but not in IL-6si cells of A549 and H157. The molecular inhibitor studies further revealed that the activation of signaling pathways, such as Stat3, Akt, MAPK, and Erk, was responsible for the up-regulation of these molecules. Further, when we treated cisplatin resistant-A549 and H157 cell lines (A549CisR and H157CisR) with a neutralizing antibody of IL-6, we observed increased cell cytotoxicity.

Conclusions and Impact: Our data support that the IL-6 signaling may be critical in conferring NSCLC cell resistance to cisplatin. In addition, we demonstrated that targeting IL-6 signaling could overcome the established acquired cisplatin resistance. Our observation supports a possible strategy to overcome cisplatin resistance through targeting IL-6 signaling or its downstream molecule(s) in treating NSCLC.